Containers are practically restricted worldwide by generally available handling techniques to typically 85,000 to 90,000 lbs gross weight. The standard container box is 9 ft. 6 in. high, 8 ft. 6 in. wide and 40, 48 or 53 feet long.
The container box is usually transported by road, on a tandem (two axle) or tridem (three axle) semitrailer hauled by a tractor rig (three axle). Allowable gross vehicle weight varies considerably by regulating authority.
Illustrative of such restrictions in North American states or provinces, generally 74,000 to 80,000 lbs sometimes 87,000 lbs (39,500 Kg) gross vehicle weight is allowed for a tandem trailer rig. When a tridem trailer is used, gross vehicle weight may be as much as 100,000 lbs (45,500 Kg), but not all regulating authorities allow heavier loading of tridem trailers, which may be restricted to as little as 74,000 lbs gross vehicle weight. The maximum gross load is thus 100,000 lbs, with maximum net payload say to 60,000 to 65,000 lbs, but may be considerably less. Fully loaded containers as noted above typically weigh 85,000 to 90,000 lbs, and cannot be economically transported by road, and in fact have to be partly unloaded.
There is therefore a need for improved more economic methods and systems of transporting fully loaded containers, which comply effectively with as many North American regulations as possible. Such methods and systems would also be widely applicable in other jurisdictions.
Containers can accommodate considerably more than 60,000 to 65,000 lbs of cargo, which represents massive underutilization of carrying capacity. A further practical restriction is that the semitrailer must stand about 47 or 48 inches above ground or highway level, to accommodate the wheel assemblies. The maximum regulated height of the loaded semitrailer is 13 ft. 6 in., in North America. Although the bed of the trailer could be lowered forward of the rear wheel assembly, this would prevent easy access to the container interior from a loading dock.
To place the container on a double trailer assembly, including lead and pup tandem trailers with articulated coupling, would increase maximum gross vehicle weight to some 125,000 lbs (56,500 Kg), and the maximum payload to some 90,000 lbs. This would represent an increase of some 25,000 to 30,000 lbs in carrying capacity or 40 to 50% increase in round figures. It is possible that use of a tridem lead trailer, would allow a maximum gross vehicle weight of some 138,000 lbs (62,500 Kg), and an even greater increase in carrying capacity. Thus far containers have been typically transported on a single trailer hauled by a rig.
Canadian Patent 1190574, issued Jul. 16, 1985, to Kleysen, teaches to carry elongate loads on conventional unmodified lead trailer pup trailer combinations, using removable swivel bunks. One swivel bunk, in normal practice the rear bunk installed on the pup trailer, is a sliding swivel bunk. Its cradle is mounted on a pivot pin. The pivot pin is slidably as well as rotationally mounted in a slot in its support allowing longitudinal motion of the cradle with respect to the support and the trailer. This conformation allows use of articulated double conventional trailers to carry a single elongate load, without undue cornering problems. The limited sliding movement of the rear swivel bunk support point on the rear pup trailer, allows the elongate load to conform as closely as possible to the tracking of the trailer wheels which follow the tractor rig wheel rack around corners.
There are three basic types of double semitrailer combinations. One is fifth wheel coupling trailer to trailer, where the fifth wheel is mounted on the lead trailer. Another is a single drawbar converter dolly coupling trailer to trailer, where the dolly is mounted beneath the pup trailer. The third is a double drawbar converter dolly coupling trailer to trailer, where the dolly is again mounted beneath the pup trailer.
It is a principal object of the invention to provide improved transport weight capacity for elongate loads, particularly containers, utilizing articulated lead pup trailer combinations. It is a subordinate object of the invention to provide such combinations, using but not restricted to fifth wheel, single drawbar converter doily, and double drawbar converter doily couplings. It is another object of the invention to provide swivel bunks on both trailers engaging the container to allow easier tracking and manoeuvring of the container double trailer combination around corners. This is a significant advantage as it makes the container double trailer combination much more manoeuvrable in city streets, where often space is very restricted. It is a further object of the invention to provide bunks integral to the trailers. It is a further object of the invention to provide a sliding swivel bunk, enabling the container to be unloaded in place on the trailer combination. It is a further object of the invention to provide means to lock the trailers in relative position. It is a further subsidiary object of the invention to provide means to lock the trailers in articulatory relationship, for highway driving. It is a further subsidiary object of the invention to provided means to lock the trailers in aligned longitudinal relationship, for backing up the combination. It is a further subordinate object to provide shortening of the double trailer combination in aligned longitudinal relationship. The locking and shortening makes for ease of backing up and unloading. It is a further subordinate object that when in aligned relationship, the rear of the container coincides with or projects beyond the rear of the pup trailer. It is a further subordinate object that the modified semitrailers of the invention comply as fully as possible with and be usable under the broadest possible range of applicable transport regulations.
To achieve this the loaded trailer train must be able to articulate, and the semitrailer height preferably must not exceed 48 inches otherwise the top of the container will exceed the 13 ft. 6 in. regulated height restriction.